Analytical method for determining volatiles, solids and solvent extractables

ABSTRACT

An apparatus and method for quantitatively measuring volatiles, solids and solvent extractables is described which provides rapid and accurate determinations using microwave heating, electronic balance weighing and solvent extracting of solubles. The method involves subjecting a weighed sample to microwave drying for a preselected time, reweighing to obtain the dry weight and determine volatile loss, solvent extracting the dried sample to determine fats, oils and other extractables followed by final measurement of residual solids. The apparatus is preferably automated to sequentially actuate the required weighing, microwave heating, solvent extraction, redrying, reweighing and calculation of the percentages of volatiles, solvent solubles and solids. The apparatus and method are particularly suited for analytical uses in the food and dairy industries.

This is a division of application Ser. No. 445,199, filed Nov. 29, 1982,now U.S. Pat. No. 4,554,132 issued Nov. 19, 1985, which in turn is acontinuation of application Ser. No. 021,986, filed Mar. 19, 1979, nowabandoned.

This invention is directed to an analytical apparatus and method fordetermining solids, volatiles and solvent extractable substancescontained in a substance and, more particularly, it is directed to amethod and apparatus for quantitatively determining moisture, solids andfat content of food products, waste products, blood and other organicmaterials.

The invention more particularly is directed to rapid quantitativeanalyses of materials which may have a high water content, which thusrequire the evaporation of such water to determine the solids and othermaterials present without removing or destroying the other materials inthe process of removing the water or moisture. In particular, the rapidanalysis is effected by the utililization of microwave heating to driveoff the moisture, followed by solvent extraction, and the determinationsof solid content and the proportions of water, solids, oils, fat, etc.,detected.

BACKGROUND OF THE INVENTION

The determination of volatiles in a given substance is a very routinedetermination which is made countless times every day in numerousindustries. Almost all agricultural products, feed grains, food productsand manufactured products, such as textiles, films, coatings, paints,etc., are sold on the basis of the solid contents, the fat or oilcontent, moisture content or combination thereof. Consequently, theseanalyses must be run literally thousands of times daily in hundreds ofindustries to determine precisely the values of the products based onthe compositions thereof. Corrections for moisture gain or loss duringthe production of a manufactured product or the storage of agriculturalproducts and the like will directly affect the value of the product.Industry has thus established standards which directly relate to thevalue of the product, with price adjustments being made for variationsin content.

The monitoring of moisture, solids, oil, fat and the like contentsrequires considerable time in quality control processing and tends toensure that a proper or desired balance is obtained in the end product.Previous quality control analyses were time consuming, often takinghours to perform single tests due to the care needed in removingmoisture, measuring fat content and the like so as not to destroy ordecompose the same during the separation process. Thus, long, timeconsuming vacuum oven drying was often utilized as well as variousviscosity, colorimetric and the like tests, based either on titrationsor other analytical procedures.

In the food industry, such as the dairy industry, the analyses of milk,cream, cheese, eggs, ice cream and the like are citical, both in meetinggovernment regulations and in ensuring the quality of the product.Elaborate testing procedures have been developed over the years such asthose set forth in the book, Chemistry and Testing of Dairy Products,4th Ed., 1977, by Henry V. Atherton and J. A. Newlander, published bythe AVI Publishing Co., Inc., Westport, Conn.

Industry, however, has long needed more accurate and rapid analyticalmethods to control the quality of these products. In the same manner,meat processing also has critical parameters of moisture and fat contentwhich must be monitored and controlled. Corn, wheat, tobacco, peanutsand other food products all are subject to quality measurementsdetermined by moisture, fat and/or oil contents which are readilydetermined by the present invention. Blood analysis to determine theproportions of triglycerides, cholesterol and solids content is animportant test to which the improved analytical procedures of thepresent invention are readily adapted. Waste products, includingeffluent streams, often require close monitoring under EnvironmentalProtection Agency Regulations to control the solids, oil, grease and thelike in such effluent streams. The present invention is ideal for suchdeterminations in a rapid and precise manner.

It is therefore an object of the present invention to provide anapparatus and a process which rapidly and precisely determine theproportion of moisture or volatiles in a given substance in a fractionof the time previously required.

It is an object of the present invention to provide a method and anapparatus for measuring the solvent extractable materials in the residueof a substance from which the moisture or volatiles have been removed.

It is a further object of the present invention to provide an apparatuswhich does not depend upon operator skill but rather, automaticallyweighs and records weight measurements as needed to measure andcalculate the volatiles removed and solubles extracted.

It is yet another object of the present invention to provide a method ofvolatilizing the moisture in a sample being analyzed without decomposingthe residual substances.

It is still another object of the present invention to provide a methodand an apparatus which will calculate the percentage of materialsvolatilized, the percentage or amount of residue material and thepercentage or amount of solvent extractable material without subjectionto human or operator error, while at the same time substantiallyreducing the testing time to minutes or seconds per analysis.

These and other objects will become apparent to those skilled in the artfrom the description of the invention which follows.

THE INVENTION

In accordance with the invention a method is provided for measuring anddetermining volatiles, solids and solvent extractable solubles in asample containing the same comprising weighing a sample to obtain aninitial weight (W_(in)), subjecting the same to microwave drying for apreselected time, reweighing said sample to determine the dry weight(W_(f1)), solvent extracting said dried sample, redrying and reweighingsaid dried, extracted sample to obtain a final weight (W_(f2)) anddetermining the volatile, solids and solvent extractables from saidobtained weights.

To effect the method of the present invention an apparatus is providedfor quantitatively determining volatiles, solids and solventextractables in a sample, comprising automatic weighing means withsample holding means, microwave heating means, solvent extracting meansand recording and calculating means, said microwave heating means beingdirected at said sample holding means, said recording means beingelectrically connected to said weighing means to sense and recordweights, said solvent extracting means communicating with said sampleholding means, and means for sequentially activating said weighing,recording, microwave heating, solvent extracting and calculating meansin a predetermined sequence to determine the proportion of saidvolatiles, solids and solvent extractables.

The sequential activation of the various means of the apparatus can beeffected by mechanical means, timing means, microprocessor means,computer means, electrical means and combinations thereof. Of these, themicroprocessor is the preferred means for controlling the function ofthe apparatus and calculating the end results.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more particularly described by reference to thedrawings in which:

FIG. 1 is a schematic diagram illustrating the program sequence of theprocess of the present invention; and

FIG. 2 is a schematic diagram of the preferred solvent extractionsystem, illustrating the manner of recycling solvent for reuse.

DETAILS OF THE INVENTION

The invention can be best understood by reference to the drawings andthe following description.

The apparatus and method of the present invention utilize an automaticbalance, preferably an electronic balance or other automatic balancemeans, which can be equipped to give an electrical signal proportionalto measured weight. The automatic balance is positioned within amicrowave heating chamber, such as a wave guide or oven, in the path ofmicrowaves generated by a magnetron. Conveniently, conventionalmicrowave ovens can be utilized, modified as described herein. Thepreferred mode of positioning the weighing means in the microwave pathis to utilize a top loading electrobalance which projects through thefloor of the microwave oven. The sensing mechanisms of the balance areconveniently positioned beneath the floor of the oven sheltered from themicrowaves. The parts of the balance projecting into the microwave pathor oven are preferably composed of materials which are transparent tomicrowaves, thereby eliminating heating of the balance parts during themicrowave heating phase. Typically, polypropylene, Teflon®,polycarbonates, polyesters and similar plastic materials are used forthe stem and balance plate or sample holder. If desired, whereadditional heat is preferred to aid in drying the sample, heatgenerating parts such as a heat generating balance plate or sampleholder or containers can be used. Glass is particularly suitable forthis purpose because it normally has sufficient mositure trapped thereinto generate heat when subjected to the microwave radiation.

The microwave oven may be of conventional design, having properradiation shielding. Alternatively, it can be of specific design toaccommodate unusual sizes or shapes of samples, as well as to allow forthe direct placement of the microwave radiation source in the oven orwave guide.

It is particularly desirable to make certain modifications ofconventional microwave ovens to improve the heating efficiency for thepresent use and to prevent excessive reflection of the microwaves backto the wave generator or magnetron, which could shorten the lifethereof. Thus, it is desirable to utilize a radiation mixer to mix anddisperse the radiation. Various radiation mixers are known in the art.Normally, they are rotating fan-like machines which reflect theradiation. Such mixers avoid the production of hot spots which coulddecompose or destroy part of the sample being tested.

Additionally, it is particularly desirable to equip the oven with otherradiation absorbing materials or isolators. Radiation absorbingmaterials will couple with the radiation being admitted in the oven andthus prevent decomposition of the sample being processed due toexcessive heat or radiation. Also, having a radiation-coupling materialpresent, reflection back to the magnetron is reduced or eliminated. Thecoupling material further helps in preventing leakage of radiation fromoven.

A preferred coupling material is water, although any other polarsubstance could be used. It is preferred to circulate the couplingmaterial through the oven in radiation transparant tubing or to utilizea reservoir from which the polar substance can be circulated and cooled.The amount of coupling material used can be thus readily regulated andadjusted to the desired volume and temperature.

Instead of using a coupling material, a radiation isolator can be used.An isolator is a terminal circuit which absorbs reflected radiation andprevents a buildup of heat. Such devices are also known in the art.

As is recognized in the art, microwave radiation is absorbed by waterand polar organic molecules, causing an increase in molecular motion.Due to the absorption of radiation energy, the water and polar solventsare heated and removed through vaporization and volatilization. Itshould be noted that when a polar material is present, other non-polarvolatiles could be removed from the sample being subjected to radiationdue to the heating effect of the polar material.

Associated with the apparatus of the present invention is solventextraction means, which are used to extract the solvent soluble materialfrom the sample after the volatiles are removed by microwave heating.The solvent extraction system can be operated as an integral part of theapparatus or as an adjunct to the microwave heating and balance system.

In the solvent extraction step of the method and apparatus, apre-selected solvent is applied to the sample, after microwave drying toremove the moisture. The solvent is used in an amount sufficient toextract the solubles from the residual sample. This can be accomplishedby several different methods. The different methods include both in situextraction of the sample while in place on the balance, or temporaryremoval of the sample from the balance during the extraction process.The method used will depend on the complexity of the apparatus used,with the more simpler apparatuses using a method wherein the sample istemporarily removed from the balance.

Because the method of the present invention does not require therecovery of the extractables for measurement but rather measures theweight loss, in situ extraction can be readily accomplished by placingthe initial sample on or in filter paper. The initial drying thus leavesthe sample deposited on the filter paper through which extractingamounts of solvent can be passed to extract the solubles. This can bereadily accomplished while the sample and filter paper are on thebalance by provided solvent feeding means and solvent draining means.

The more preferred method involves removal of the dried sample from thebalance for extraction of the solubles. Again, the sample is initiallydried on filter paper and the filter paper temporarily removed from thebalance to effect the solvent extraction. When filter paper or pad isused in the process of this invention, it is preferable to use glassfiber filter paper because it not only aids in microwave heating byabsorbing microwaves, but it does not have a water content which isvolatilized and thus would affect the measurements made. The removeddried sample material on the filter is placed in a solvent bath tothereby leach and extract the soluble substances. Preferably, thesolvent bath is agitated or subjected to ultrasonic vibration tosubstantially reduce the extraction time.

The most preferred method of solvent extraction involves taring an extrafilter pad with the initial sample being placed on the first filter padout of contact with the extra filter pad. After the initial sampledrying, the filter pad with the dried sample is removed from thebalance, placed in the extracting solvent and ground by high speedshearing. This action rapidly extracts the solubles. The solvent andground pad are then filtered through the extra filter pad to therebyrecover the solids and the first filter pad. A rinse of additionalsolvent can be used to ensure recovery of all solids. The filter pad andcollected solids are then returned to the balance.

In FIG. 2, set forth in the preferred sequence, a dried sample, issubjected to grinding, solvent extraction, and filtering to recover thesolids, which are then redried and reweighed with the apparatus of thepresent invention. The used solvent is cycled through a distillationreboiler, with the vapors being collected as clean solvent in areservoir for subsequent reuse in another solvent extraction.

The solvents utilized herewith are selected for their capability ofextracting the particular extractable material which is known to bepresent in the dried sample. Depending on the particular type of sampleswhich are expected to be analyzed, the solvents can be chosenaccordingly or a more universal solvent utilized which is effective on abroad variety of samples. Typical solvents include ether, methylenechloride, carbon tetrachloride, acetone, methanol, ethanol, variousFreons®, particularly trichlorotrifluoroethane, combinations of Freonwith acetone, ethanol and the like, as well as combinations of Freon andmethylene chloride, particularly the azeotropic compositions becausethey are more readily recovered through automatic distillation andrecycling systems, as set forth herein.

It is particularly desirable to utilize nonflammable solvents, of whichan azeotropic composition of Freon plus methylene chloride in a ratio of50.5 Freon (trichlorotrifluoroethane) to 49.5 methylene chloride isparticularly preferred. This combination is an excellent solvent formost fats and oils, is relatively low boiling for easy redistillationand recovery, has good stability and therefore is particularly suitablefor the present invention.

The apparatus of the present invention can be controlled by a number ofmeans as set forth above, such as timers, electrical circuits, etc., butthe preferred method of control is by means of a microprocessor, whichis programmed to perform the functions of the apparatus in the desiredsequence and to store the electrical signals from the electrobalance forsubsequent calculations of the proportions of volatiles, extractablesand solids. A further particularly desirable apparatus which can bemodified as set forth herein to carry out the process of the presentinvention is that described in U.S. Pat. No. 3,909,598, which isincorporated herein by reference.

The process of the present invention commences by the operator placing asample to be tested in the sample holder on the electronic balance,closing the microwave oven and initiating the start of the process bypushing a start button. The sample to be analyzed is preferably evenlydistributed on some type of medium, such as a filter pad, to increasesurface area exposure and to provide a convenient holding surface forthe residual solids which will be produced during the process.Particularly suitable for this use are particulate glass substrates suchas fiber glass filters, glass fiber filter pads or glass beads, becausethese materials have no moisture regain and provide good media on whichto distribute the sample, with maximized surface area exposure.

The sample size can vary with the instrument size, electronic balanceweight range and accuracy of the test results desired. The electronicbalance and microwave oven is likewise sized for the intended usage. Itshould be noted that the basic usage of the present apparatus will beprimarily for analytical purposes and, as such, analytical weight rangesand sizes are normally used. The apparatus is therefore best sized suchthat the sample will give at least about 100 milligram weight loss forthe preferred electronic balance. This means that with a materialcontaining 5 percent moisture, the minimum sample size would preferablybe about 5 grams. With larger moisture losses and about 5 percentextractables, the weight could also be about the same amount. The sizeof the sample should be adequate to give a weight change of the lesseringredient well within the sensitivity of the balance. It is, of course,readily apparent that more sensitive electronic balances can be used forsmaller samples, but such are generally impractical except forspecialized usages. Therefore, the preferred sample weight willgenerally range between about 1 and 40 grams for most tests, dependingon the amount of extractables and volatiles actually present. Weights upto about 1,000 grams or more can be used with proper sizing of theelectronic balance

With the sample in place, the process of the present invention proceedsaccording to FIG. 1, the sequence of which is programmed into themicroprocessor. The initiation by the operator of the test causes theapparatus to sense and store the initial sample weight (W_(in)),followed by the initiation of the microwave drying. The drying time ispre-selected, based on such factors as the sample size, the magnetroncapabilities, the expected volatiles loss, time to achieve such loss,and other factors which can be readily determined by experimentation.Normally, for the average sample, microwave drying would be effected infrom 20 seconds to about 10 minutes, with longer times being requiredfor higher percentages of volatiles or other factors such as thosealready noted. The particular drying time required is largely dependentupon the radiation absorption coefficient for the particular volatilematerial.

Having effected the microwave heating and drying for the pre-selectedtime, the weight of the sample is again sensed and stored by themicroprocessor to provide a weight (W_(f1)).

The solvent extraction of the sample is then effected as previouslydescribed. The extracted sample is then re-dried by again subjecting itto a short period of microwave heating. The amount of heating requireddepends on the solvent utilized but normally such heating cycles can berelatively short due to the volatility of the solvents normally used. Oncompletion of the redrying, the microprocessor again senses and storesthe weight of the redried sample as W_(f2). The proportions of thevarious components are thus readily calculated as follows by thefollowing equations: ##EQU1##

Such computations can be calculated, either by the microprocessor or bythe operator, with the preferred method being by the microprocessor,which then displays the calculation in readable form.

The readable form can be in any of various known forms such as printedcopy, digital panel meter readings, direct electrical feed to otherinstruments, and the like. A preferred mode of readout is the digitalpanel meter. Such meters, used in conjunction with the visibleindicators are particularly helpful in normal testing procedures.Indicators designated by code, numerals, lights or the like signal theparticular readout being shown on the digital panel meter. Such readoutscan include initial sample weight, sample weight after initial drying,sample weight after solvent extraction, final sample weight, thedifferences between sample weights, and the percent weight loss orpercent volatiles, and percent extractables of the sample.

It is also convenient to provide operator controls having memory recallsuch that any one or more of the noted measurements can be recalled.Such recall is useful when the operator may want to recheck the initialweight and weight changes to check calculations. Push buttons orelectrical switches can be provided so that the operator can re-examinethese data on the digital panel meter. Where a printout reader is used,such recall is not necessary since the readout is on a printed copy.

The present apparatus is particularly advantageous for use in the dairyindustry such as in the analysis of milk, cream, cheese, ice cream andthe like because of its high speed and accuracy. Total determinationsincluding moisture, solids and fat content generally require less than 5minutes. The accuracy is precise because it involves a directmeasurement, which is extremely accurate. In many cases, fat content isdefined on the basis of solvent soluble material. Direct measurementseliminate the need for a calibration. The precision of the tests andapparatus is excellent because of the high resolution of electronicbalances which are incorporated within the present apparatus.

While the present apparatus and method have been described moreparticularly with respect to an analytical instrument, it is recongnizedthat this apparatus and method can be readily adapted for other usessuch as in-line production control, production uses, the preparation ofdried samples for further testing, and other end uses, as may berequired in various commercial industrial processes. Consequently, thepresent invention is not intended to be limited except as noted in theappended claims.

What is claimed is:
 1. A method for determining amounts of volatiles, solids, and solvent extractable solid in a sample containing the same comprising placing the sample to be analyzed on a sample holder substrate, weighing said sample holder substrate with the sample thereon to obtain the sample's initial weight (W_(in)), subjecting the sample on the sample holder substrate to microwave drying for a preselected time to dry the sample, reweighing said sample holder substrate with the dried sample thereon to obtain the sample's dry weight (W_(f1)), extracting said dried sample and said sample holder substrate with a solvent under high speed shearing conditions, recovering said solvent extracted sample and sample holder substrate, redrying said solvent extracted sample and sample holder substrate, and weighing said solvent extracted and redried sample and sample holder substrate to obtain the sample's final weight (W_(f2)), and determining the the amount of volatiles, solids, and solvent extractable solids in said sample from said obtained weights.
 2. The method of claim 1 wherein the sample holder substrate is a glass fiber substrate.
 3. The method of claim 2 wherein the glass fiber substrate is a glass fiber filter pad.
 4. A method for determining amounts of volatiles, solids, and solvent extractable solids in a sample containing the same comprising taring a first and a second filter pad on a balance, placing the sample to be analyzed on said first filter pad, weighing said first filter pad with the sample thereon to obtain the sample's initial weight (W_(in)), subjecting the sample on the first filter pad to microwave drying for a preselected time to dry the sample, reweighing said first filter pad with the dried sample thereon to obtain the sample's dry weight (W_(f1)), extracting said dried sample and said first filter pad with a solvent while subjecting said dried sample and said first filter pad to agitation sufficient to shear and shred said dried sample and said first filter pad, recovering said sheared, shredded, and solvent extracted sample and first filter pad on said second filter pad, microwave redrying said sheared, shredded, and solvent extracted sample and first filter pad on said second filter pad, and weighing said second filter pad with said sheared, shredded, solvent extracted, and redried sample and first filter pad thereon to obtain the sample's final weight (W_(f2)), and determining the amounts of volatiles, solids, and solvent extractable solids in said sample from said obtained weights.
 5. The method of claim 4 wherein the percentage of volatiles in the sample is determined usins the expression ##EQU2##
 6. The method of claim 4 wherein the percentage of solids in the sample is determined using the expression ##EQU3##
 7. The method of claim 4 wherein the percentage of solvent extractable solids in the sample is determined using the expression ##EQU4##
 8. The method of claim 4 wherein after the step of recovering said sheared, shredded, and solvent extracted sample and first filter pad on said second filter pad, the solvent is recycled by distillation and then recovered for reuse.
 9. The method of claim 4 wherein the first and second filter pads are glass fiber pads.
 10. The method of claim 4 wherein the solvent is an azeotropic composition of trichlorotrifluoroethane and methylene chloride.
 11. The method of claim 4 wherein the sample is a food product.
 12. The method of claim 11 wherein the sample is a dairy product. 